Properties of mitomycin C-sensitive mutants of Escherichia coli K-12.

Strains hypersensitive to mitomycin C (MC) were isolated from Escherichia coli K-12 after treatment with nitrosoguanidine. Of 43 MC-sensitive strains tested for their ultraviolet light (UV) sensitivity and for their ability to reactivate UV-inactivated lambda phage, 38 were found to be insensitive to UV irradiation and to be able to reactivate UV-irradiated bacteriophage lambda. Some properties of the MC-sensitive, uvr(+) mutants were analyzed. Synthesis of deoxyribonucleic acid (DNA) in MC-sensitive, uvr(+) mutants was inhibited at a lower concentration of MC than in the wild-type strain. Mutant cells, labeled with (3)H-thymidine and then exposed to MC, released radioactivity as low molecular weight compounds. The amount of radioactivity released was the same as that from the wild-type strain. MC-sensitive, uvr(+) mutants, as well as the corresponding wild-type strain, were equally susceptible to induction of prophage phi80 by UV irradiation. However, MC induction of prophage was achieved in MC-sensitive, uvr(+) mutants at a lower concentration of the antibiotic than in the wild-type strain. Genetic experiments indicated that a gene controlling MC sensitivity is located close to that determining lactose fermentation of E. coli. It is situated on episome F'13, and the wild type is dominant to the MC-sensitive allele.